This invention relates generally to space vehicles and, in greater particularity, relates to a device and method of protecting selected surfaces on the space vehicle from external incident radiant energy.
Many satellite components require temperature control within a narrow band to assure long life and correct operation. One temperature control method is to enclose the instrument either singly or in a group inside a chamber which is designed to have good internal thermal coupling so as to give near uniform internal temperature. One side of the chamber is a radiator: a good conductor which is thermally coupled to heat sources inside the chamber and which has a high emissivity surface facing dark space. Finally, this radiator is covered by louver blades arranged so they can be opened or closed, exposing or covering the radiator. Rectangular blades in a venetian blind like arrangement are illustrated in FIGS. 1 and 2. A pinwheel arrangement has also been used. In either case, a bimetallic coil spring, thermally coupled to the radiator senses the temperature of the radiator, opening the louver when the radiator is warm and closing it when the radiator is cool with respect to the control range, and generally finding an intermediate position to maintain the specified temperature. This thermo-mechanical mode of operation is called the “passive mode.”
More precise control of the radiator temperature is accomplished by adding an electronic device to sense the radiator temperature and to control an electric current to a heater which is bonded onto the bimetallic coil. This “active mode” gives greater rotation of the louver per unit temperature change due to its amplification and accomplishes quicker, more precise temperature control; solar and earth albedo energy are prevented from entering the louver by three methods:                (1) keeping the radiator surface always directed toward dark space,        (2) providing a thermal fence to shield the radiator, and        (3) coating the radiator and louver blades with a material which gives a low solar absorptivity while still giving high emissivity.        
If hostile high energy radiation such as a laser beam is directed at the louver, it presents a dual threat:                (1) the energy may be absorbed into the exposed surface materials, heating them until they are destroyed, and        (2) as the radiant energy heats the exposed surfaces, that heat is conducted to the bimetallic coil springs causing the coil springs to open the louver completely exposing the radiator and admitting even more radiation. Then, the thermal control louver is rendered inoperative and more radiant energy is admitted directly into the radiator.        
Existing louvered radiator designs are extremely vulnerable to laser attack because of the light weight materials generally used, the sensitivity of their performance to the radiative characteristics of their surface, and in some cases, the fundamental conflict between radiative characteristics desirable for their normal function and those desirable for rejecting laser radiation.
These drawbacks have motivated the search for alternative devices which can prevent laser damage to radiators in space.